1. Field of the Invention
The invention relates to a polymeric composition for making aqueous polymeric dispersions and, more particularly, to an aqueous polymer dispersion comprising such a polymeric composition; the use of a polymeric composition for making a coating composition, a printing ink, an adhesive, a sealant or caulking material; an aqueous coating composition; and a process for manufacture thereof.
2. Description of the Related Art
The use of polymer-based coatings to protect surfaces and enhance the aesthetic and functional properties of materials is well known.
Waterborne compositions are widely used to manufacture and apply such coatings because of their low VOC (Volatile Organic Compound) content as compared to solventborne compositions. However, some of the advantageous characteristics of the solventborne compositions have been difficult to attain with waterborne compositions. For example, high gloss durable finishes have proved elusive due to poor film coalescence, in particular in acrylic emulsions, and poor hydrolytic stability, in particular in water-reducible resins.
U.S. Pat. No. 5,698,625 discloses a process for the preparation of water-dilutable, air-drying coating binders based on acrylic modified and vinyl modified alkyd resin emulsions. The alkyd resin resulting from the disclosed process comprises hydrophilic groups grafted onto an alkyd by ester linkages. It is believed that the ester linkage at the boundary between the alkyd and the hydrophilic groups has a poor hydrolytic stability and that this leads to poor emulsion stability due to loss of the hydrophilic groups from the alkyd.
GB2413330 discloses an aqueous composition comprising at least one vinyl graft copolymer (A) and at least one vinyl polymer (B), where vinyl polymer (B) is more hydrophobic than vinyl graft copolymer (A). According to the examples vinyl graft copolymer (A) is obtained with a two step process. First a macromonomer is formed by reacting vinyl monomers in the presence of a cobalt catalyst and then free radical polymerizing this with vinyl monomers to provide a vinyl graft copolymer (A). Next vinyl copolymer (B) is formed in the presence of (A) by free radical polymerization of vinyl monomers. Polymer (B) is not grafted to copolymer (A) so that in the resulting mixture there is no hydrophilic polymeric chain grafted to a hydrophobic polymer.
WO 99/45078 discloses a water based dispersion useful for forming aqueous coating compositions. The problem addressed by WO99/45078 is the dispersion of hydrophobic materials such as melamine resins, hydrophobic polyesters, hydrophobic acrylic polymers, hydrophobic polyurethanes and blocked organic polyisocyanates in aqueous solution. The proposed solution to the problem is the use of a dispersant in the form of a branched polymer comprising a hydrophilic backbone and side chain hydrophilic macromonomer branches appended thereto. The dispersion is formed by mixing together the dispersant and the hydrophobic material by agitation before dispersion of the two components in water. In the resulting dispersion there is no grafting between the dispersant branched polymer and the hydrophobic material which is to be dispersed. This leads to a lack of stability of the aqueous dispersion and poor water resistance of the dried film.
Resydrol AY 586 is an example of a commercially available aqueous alkyd dispersion representing the state of the art. In comparison to this state of the art dispersion, the dispersion of the present invention exhibits improved stability, exemplified by a minimal pH drift and change in viscosity after 28 days under hot room conditions (120 F). For a more detailed description see example 16 of the present application.